1. Field of the Invention
The present invention relates to power converter circuits, and more particularly, to an unregulated DC-to-DC power converter suitable for intermediate bus applications in which synchronous rectifiers are efficiently driven to provide faster transition time and reduced loss.
2. Description of Related Art
With the increasing complexity of electronic systems, it is common for an electronic system to require power provided at several different discrete voltage and current levels. For example, electronic systems may include discrete circuits that require voltages such as 3 v, 5 v, 9 v, etc. Further, many of these circuits require a relatively low voltage (e.g., 1 v), but with relatively high current (e.g., 100 A). Since it is undesirable to deliver relatively high current at low voltages over a relatively long distance through an electronic device, it is known to distribute an intermediate bus voltage throughout the electronic system, and include an individual point-of-load (“POL”) regulator, i.e., DC/DC converter, at the point of power consumption within the electronic system. Particularly, a POL regulator would be included with each respective electronic circuit to convert the intermediate bus voltage to the level required by the electronic circuit. An electronic system may include multiple POL regulators to convert the intermediate bus voltage into each of the multiple voltage levels. Ideally, the POL regulator would be physically located adjacent to the corresponding electronic circuit so as to minimize the length of the low voltage, high current lines through the electronic system. The intermediate bus voltage can be delivered to the multiple POL regulators using low current lines that minimize loss.
Typically, a separate power converter would provide an isolated intermediate bus voltage (e.g., 9 volts) from a relatively higher nominal input voltage source (e.g., 48 volts). As long as the input voltage source is regulated, the intermediate bus voltage converter can be unregulated. A conventional intermediate bus voltage converter includes a transformer to provide isolation between the input and output voltages. On the output side of the transformer, synchronous rectifiers convert the periodic voltage on the transformer to a DC output voltage. In view of their low on state resistance, the synchronous rectifiers are typically provided by field effect transistors (FETs). Since the periodic voltage on the transformer comprises a 100% duty cycle without intermediate zero voltage states, the synchronous rectifiers can be triggered by voltage transitions across the transformer. But, a drawback of the conventional intermediate bus voltage converter is that the synchronous rectifiers are slow to transition between on and off states, causing them to sink current to ground before settling in the off state. This results in a reduction of efficiency of the intermediate bus voltage converter, which is exacerbated when the converter is operating at a low or no load condition.
Thus, it would be advantageous to have an unregulated DC-to-DC power converter suitable for intermediate bus voltage converter applications in which the synchronous rectifiers are driven efficiently to provide faster transition time and reduced loss.